Blade Steel Basics
- September 22, 2020
- Good To Know
When you are considering buying a knife you should pay a lot of attention to the type of steel used in the blade. Blade steel is a very important factor that determines how well a knife will perform. While blade steel is a very important factor to consider when buying a knife, there are several other factors to consider that will influence blade performance, like the heat treat, blade geometry, cutting tasks, and sharpening. I will discuss those factors in later blogs. For the purpose of this blog, I will discuss the five properties within the steel that determines the attributes, and performance of the steel used in the blade.
Hardness is the ability to resist deforming when subject to stress and applied forces. Hardness in the knife steel is directly correlated to strength and is generally measured using the Rockwell C scale (HRC). You want a durable knife blade that won’t bend because the steel is too soft, and you don’t want a steel that’s so hard that it becomes brittle and is susceptible to chipping. For most knife tasks/applications you will want a hardness rating between 56RC and 62RC. You can find knives with the blade steel as high as 66RC, but keep in mind that the harder the blade steel, the more challenging it will be to sharpen.
Toughness is the ability to resist damage like cracks or chips when subject to impact or “sudden loads”. In general, the harder the steel the less tough it’s likely to be, and may be thought of as the opposite of brittleness. Toughness testing is not as standardized as hardness testing. Common toughness tests include various impact tests and bend fracture tests.
Wear resistance is the steel’s ability to withstand damage from both abrasive and adhesive wear. Abrasive wear occurs when harder particles pass over a softer surface. Adhesive wear occurs when debris is dislodged from one surface and attaches to the other. Wear resistance generally correlates with the steel’s hardness but is also heavily influenced by the specific chemistry (elements) of the steel. In steels of equal hardness, the steel with larger carbides will typically resist wear better. However, carbides can become brittle and crack, thus decreasing toughness.
Corrosion resistance is the ability to resist corrosion such as rust caused by external elements like humidity, moisture and salt. These elements can cause significant damage to certain types of knife steels. From a corrosion resistance perspective you have two types of steels used in knife blades, stainless and non-stainless. Non-stainless steel knives need oil and maintenance to keep rust /corrosion away. Stainless steel knives are more forgiving, but they can still end up rusting if neglected. The stainless steel classification is generally misleading because almost all types of steel will show some kind of discoloration if left exposed to the elements long enough. Note: A high resistance to corrosion usually sacrifices the overall edge performance (Edge Retention).
Edge Retention represents how long the blade will retain its sharpness when subject to periods of use. You want a knife that you can get sharp and stay sharp through repeated use. Edge retention is a combination of wear resistance that resists edge deformation (blunting). Edge retention lacks any defined set of standards and is subjective to the user. Keep in mind that there are other factors that will determine edge retention…. edge (bevel) angle, user abuse, and the material being cut or sliced.
In reality, there is no perfect blade steel just like there is no perfect knife. There is a trade off when trying to optimize any one of the above properties. The biggest trade off is balancing hardness/strength with toughness. Some blades can be made to be exceptionally hard but will be susceptible to chipping or cracking. Some blades can be extremely tough and able to bend, but will lose it’s edge retention quickly. Knowing what tasks and how you plan to use your knife, you can compare the levels of metallurgical properties (elements) offered in different steels. This will help determine which steels are best suited for obtaining the desired blade performance you are seeking.